Pluralization, Gender, and ICU Message Formatting
Handle plurals, select cases, and parameterized strings using the ICU message syntax.
Pluralization, Gender, and ICU Message Formatting is a free Flutter Mobile Development lesson on CoddyKit — lesson 2 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Flutter Mobile Development learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Why ICU Messages Matter
Translating an app is more than swapping words. Different languages pluralize, gender, and order words differently. A naive string like "$count items" reads wrong as "1 items", and many languages have several plural forms.
Flutter solves this with ICU message syntax (International Components for Unicode), the same standard used across the industry. You write one message with rules for plurals, select/gender, and placeholders, and the right form is chosen at runtime per locale.
plural— pick a form based on a numberselect— pick a branch based on a string (e.g. gender)- placeholders — inject typed values like names, dates, numbers
The ARB File: Where Messages Live
Flutter's flutter_localizations + intl toolchain reads ARB files (Application Resource Bundle). Each locale has its own file: app_en.arb, app_tr.arb, etc.
An ARB entry has a key, a value (the ICU message), and an optional @key metadata object describing placeholders.
- Keys become generated Dart getters/methods.
- The
@keyblock declares each placeholder'stypeand optionalformat.
{
"appTitle": "My Shop",
"@appTitle": {
"description": "The title shown in the app bar"
},
"welcome": "Welcome, {name}!",
"@welcome": {
"placeholders": {
"name": { "type": "String" }
}
}
}Simple Placeholders
A placeholder is written in curly braces inside the message: {name}. The generated Dart code becomes a method whose parameter matches the placeholder name.
After enabling generate: true in pubspec.yaml and running flutter gen-l10n, you call it through AppLocalizations.
// app_en.arb
// "welcome": "Welcome, {name}!"
import 'package:flutter/material.dart';
import 'package:flutter_gen/gen_l10n/app_localizations.dart';
Widget build(BuildContext context) {
final l10n = AppLocalizations.of(context)!;
return Text(l10n.welcome('Aylin')); // -> "Welcome, Aylin!"
}Pluralization with ICU
The plural form picks a branch based on a number argument. Syntax: {count, plural, ...categories...}.
ICU plural categories are =0, =1, zero, one, two, few, many, other. The other branch is mandatory — it is the fallback when no other category matches. Use # to print the number itself.
=0,=1match the exact value.one,few,manyare language-defined categories (English only usesoneandother).
{
"itemsInCart": "{count, plural, =0{Your cart is empty} =1{1 item in cart} other{# items in cart}}",
"@itemsInCart": {
"placeholders": {
"count": { "type": "int" }
}
}
}Calling a Plural Message
The generated method takes the count argument. The framework selects the correct branch for the active locale automatically.
Notice that English only ever needs one/other, but a locale like Polish or Arabic will use few/many in its own ARB file — your Dart call site does not change.
final l10n = AppLocalizations.of(context)!;
Text(l10n.itemsInCart(0)); // "Your cart is empty"
Text(l10n.itemsInCart(1)); // "1 item in cart"
Text(l10n.itemsInCart(7)); // "7 items in cart"Why '=1' and 'one' Are Different
A common confusion: =1 is an exact value match, while one is a language plural category. They are not the same.
=1matches only the literal number 1.onematches whatever the locale's CLDR rules call the "one" category. In English that is just 1, but in some locales theonecategory also covers values like 21, 31, etc.
Best practice: provide other always; add one for natural singular/plural; use =0/=1 only when you need special wording ("empty", "no messages") that differs from the grammatical plural.
Gender and the 'select' Form
The select form branches on a string value rather than a number. The classic use is grammatical gender, which changes pronouns and verb agreement in many languages.
Syntax: {gender, select, male{...} female{...} other{...}}. Like plural, other is required as the fallback (and handles unknown/non-binary values gracefully).
{
"sharedPhoto": "{gender, select, male{He shared a photo} female{She shared a photo} other{They shared a photo}}",
"@sharedPhoto": {
"placeholders": {
"gender": { "type": "String" }
}
}
}Demonstrating select() in Pure Dart
You don't need Flutter to understand the intl primitives. The Intl.select function mirrors what the generated code does: it maps a key to a branch with an other fallback.
This standalone program shows the selection logic, including the fallback when an unexpected value arrives.
import 'package:intl/intl.dart';
String sharedPhoto(String gender) {
return Intl.select(gender, {
'male': 'He shared a photo',
'female': 'She shared a photo',
'other': 'They shared a photo',
}, name: 'sharedPhoto', args: [gender]);
}
void main() {
print(sharedPhoto('male')); // He shared a photo
print(sharedPhoto('female')); // She shared a photo
print(sharedPhoto('unknown')); // They shared a photo (fallback)
}Combining Gender and Plurals (Nesting)
ICU lets you nest a plural inside a select (or vice versa) to handle messages that vary by both gender and count. Place one block inside a branch of the other.
Keep nesting shallow — deeply nested messages are painful for translators. If it gets complex, consider splitting into separate keys.
{
"likes": "{gender, select, female{She got {count, plural, =0{no likes} =1{1 like} other{# likes}}} male{He got {count, plural, =0{no likes} =1{1 like} other{# likes}}} other{They got {count, plural, =0{no likes} =1{1 like} other{# likes}}}}",
"@likes": {
"placeholders": {
"gender": { "type": "String" },
"count": { "type": "int" }
}
}
}Formatted Placeholders: Numbers and Dates
Placeholders can be formatted per locale using the format field in metadata. Numbers use formats like decimalPattern or currency; dates use DateFormat skeletons such as yMMMd.
This means 1234.5 renders as 1,234.5 in en-US but 1.234,5 in many European locales — automatically.
{
"price": "Total: {amount}",
"@price": {
"placeholders": {
"amount": {
"type": "double",
"format": "currency",
"optionalParameters": { "symbol": "\u20ac", "decimalDigits": 2 }
}
}
},
"lastSeen": "Last seen {when}",
"@lastSeen": {
"placeholders": {
"when": { "type": "DateTime", "format": "yMMMd" }
}
}
}Formatting Numbers and Dates in Plain Dart
The same intl formatters power those ARB format fields. Here is a runnable program using NumberFormat and DateFormat directly, the way the generated localization code does under the hood.
import 'package:intl/intl.dart';
void main() {
final amount = 1234.5;
final usd = NumberFormat.currency(locale: 'en_US', symbol: '\$');
final eur = NumberFormat.currency(locale: 'de_DE', symbol: '\u20ac');
print(usd.format(amount)); // \$1,234.50
print(eur.format(amount)); // 1.234,50 \u20ac
final date = DateTime(2026, 6, 10);
print(DateFormat.yMMMd('en_US').format(date)); // Jun 10, 2026
print(DateFormat.yMMMd('tr_TR').format(date)); // 10 Haz 2026
}Quick Check: Choosing the Right Form
You need a message that says "no messages", "1 message", or "N messages" depending on a count, and you want it to also work correctly in locales with few/many categories. Which approach is correct?
Recap
You now know how to localize dynamic text in Flutter with ICU message syntax:
- ARB files hold messages per locale;
@keymetadata declares placeholder types and formats. - Placeholders
{name}inject typed values into messages. - plural
{count, plural, =0{} =1{} other{}}picks a form by number;otheris mandatory and#prints the value. - =1 vs one: exact-value match versus language plural category — use exact matches only for special wording.
- select
{gender, select, male{} female{} other{}}branches on a string; great for gender. - Nesting combines gender and count when needed.
- format metadata +
NumberFormat/DateFormatrender numbers and dates per locale.
Write messages so translators control wording per language while your Dart call sites stay unchanged.
Frequently asked questions
Is the “Pluralization, Gender, and ICU Message Formatting” lesson free?
Yes — the full text of “Pluralization, Gender, and ICU Message Formatting” is free to read here on the web, and the Flutter Mobile Development course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Flutter Mobile Development course, upgrade to CoddyKit PRO.
What will I learn in “Pluralization, Gender, and ICU Message Formatting”?
Handle plurals, select cases, and parameterized strings using the ICU message syntax. You practise Flutter Mobile Development with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Flutter Mobile Development?
No prior experience is required. Flutter Mobile Development on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Pluralization, Gender, and ICU Message Formatting” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Flutter Mobile Development lesson?
Yes. Every Flutter Mobile Development lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- ARB Files and gen_l10n Localization Workflow
- Pluralization, Gender, and ICU Message Formatting
- RTL Layouts and Directionality Handling
- Semantics, Screen Readers, and Accessible Widgets